1. Field of the Invention
The present invention relates to a spacer to be used in a flat-panel type display and a flat-panel type display incorporated with the spacer.
2. Description of the Related Art
Various flat-panel type displays have been researched as image displays alternative to the cathode ray tube (CRT). Examples of such flat-panel type displays may include a liquid crystal display (LCD), an electroluminescent display (ELD), and a plasma display panel (PDP). Furthermore, a flat-panel type display incorporated with an electron emission element is under development. Cold-cathode field electron emission elements, metal/insulating film/metal type elements (may be referred to as MIM elements) and surface-conduction type electron emission elements are known as electron emission elements. The flat-panel type displays incorporated with electron emission elements including these cold-cathode electron sources have attracted attention from the view point of high resolution, high-brightness color display and low power consumption.
In general, a cold-cathode field electron emission display (hereafter may be abbreviated as a display) serving as a flat-panel type display incorporated with a cold-cathode field electron emission element has a configuration in which a cathode panel and an anode panel are opposed to each other with a space maintained under vacuum therebetween, wherein the cathode panel has an electron emission region corresponding to each of subpixels arrayed in a two-dimensional matrix, and the anode panel has a luminescent layer that emits light through excitation due to collision with electrons emitted from the electron emission region. In general, at least one cold-cathode field electron emission element (hereafter may be abbreviated as a field emission element) is disposed in the electron emission region. Examples of electron emission elements may include a Spindt type, a flat type, an edge type, and a planar type.
FIG. 5 is a conceptual partial end view of an example of a display having a Spindt type field emission element. FIG. 6 is a schematic perspective exploded view of a part of a cathode panel CP and an anode panel AP when the cathode panel CP and the anode panel AP are disassembled. The Spindt type field emission element constituting this display is composed of a cathode 11 disposed on a support 10, an insulating layer 12 disposed on the support 10 and the cathode 11, a gate electrode 13 disposed on the insulating layer 12, openings 14 disposed in the gate electrode 13 and the insulating layer 12 (first openings 14A disposed in the gate electrode 13 and second openings 14B disposed in the insulating layer 12), and conical electron emission portions 15 disposed on the cathode 11 positioned at the bottoms of the openings 14.
In this display, the cathode 11 is in the shape of a band extending in a first direction (the Y direction shown in FIG. 5 and FIG. 6), and the gate electrode 13 is in the shape of a band extending in a second direction (the X direction shown in FIG. 5 and FIG. 6) different from the first direction. In general, each of the cathode 11 and the gate electrode 13 is formed into the shape of a band in such a way that the directions of the projected images of the two electrodes 11 and 13 become orthogonal to each other. The region where the band-shaped cathode 11 and the band-shaped gate electrode 13 overlap each other is an electron emission region EA corresponding to the region of one subpixel. Such electron emission regions EA are usually arrayed in a two-dimensional matrix in the effective region (the region corresponding to the display region of the display) of the cathode panel CP.
On the other hand, the anode panel AP has a structure in which luminescent layers 22 (specifically, red-emitting luminescent layers 22R, green-emitting luminescent layers 22G, and blue-emitting luminescent layers 22B) in a predetermined pattern are disposed on a substrate 20, and the luminescent layers 22 are covered with an anode 24. Spaces between these luminescent layers 22 are filled with light absorbing layers (black matrix) 23 formed from a light absorbing material, e.g., carbon, and thereby, an occurrence of color blurring of a displayed image or an occurrence of optical crosstalk may be prevented. In the drawings, reference numeral 21 denotes a partition wall, reference numeral 40 denotes, for example, a tabular spacer, reference numeral 25 denotes a spacer holding portion, reference numeral 26 denotes a bonding component formed from a bonding material, e.g., frit glass, reference numeral 16 denotes an interlayer insulating layer, and reference numeral 17 denotes a focusing electrode. In FIG. 6, the partition wall, the spacer, the spacer holding portion, the focusing electrode, and the interlayer insulating layer are omitted.
The anode 24 has a function as a reflective film for reflecting the light emitted from the luminescent layer 22 and, furthermore, a function of preventing charging of the luminescent layer 22. The partition wall 21 has a function of preventing an occurrence of so-called optical crosstalk (color blurring) due to collision of electrons recoiling from the luminescent layer 22 or secondary electrons emitted from the luminescent layer 22 (hereafter these electrons are collectively referred to as backscattered electrons) with the other luminescent layers 22.
Each subpixel is composed of an electron emission region EA on the cathode panel side and a luminescent layer 22 on the anode panel side facing a group of these field emission elements. In the display for performing color display, each pixel is composed of a set of one red-emitting luminescent layer, one green-emitting luminescent layer, and one blue-emitting luminescent layer. The above-described pixels of the order of a few hundreds of thousands to a few millions, for example, are arrayed in the effective region.
The anode panel AP and the cathode panel CP are arranged in such a way that the electron emission region EA and the luminescent layer 22 are opposed to each other, the marginal portions are bonded with the bonding component 26 therebetween, and evacuation is performed, followed by sealing, so that a display is produced. The space surrounded by the anode panel AP, the cathode panel CP, and the bonding component 26 is under high vacuum (for example, 1×10−3 Pa or less).
Therefore, the display may be damaged by atmospheric pressure unless the spacers 40 are disposed between the anode panel AP and the cathode panel CP. The spacer 40 is composed of a substrate of spacer 40A and an antistatic coating 40B disposed on the side surface portion of the substrate of spacer 40A. These will be described later.
A relatively negative voltage is applied to the cathode 11 from a cathode control circuit 31, a relatively positive voltage is applied to the gate electrode 13 from a gate electrode control circuit 32, a relatively negative voltage (for example, 0 volts) is applied to the focusing electrode 17 from a focusing electrode control circuit (not shown in the drawing), and a positive voltage further higher than the voltage of the gate electrode 13 is applied to the anode 24 from an anode control circuit 33. In the case where display is performed in the above-described display, for example, a scanning signal is input into the cathode 11 from the cathode control circuit 31, and a video signal is input into the gate electrode 13 from the gate electrode control circuit 32. Alternatively, a video signal is input into the cathode 11 from the cathode control circuit 31, and a scanning signal is input into the gate electrode 13 from the gate electrode control circuit 32. Electrons are emitted from the electron emission portion 15 on the basis of the quantum tunnel effect by an electric field generated when a voltage is applied between the cathode 11 and the gate electrode 13, the electrons are attracted to the anode 24 and pass through the anode 24, so as to collide with the luminescent layer 22. As a result, the luminescent layer 22 is excited and emits light, so that a desired image is obtained. That is, the operation of this cold-cathode field electron emission display is basically controlled by the voltage applied to the gate electrode 13 and the voltage applied to the cathode 11.
The substrate of spacer 40A constituting the spacer 40 is formed from a rigid material, e.g., glass or ceramic. The two ends of the spacer 40 are in contact with the anode 24 and the focusing electrode 17, respectively. Consequently, a potential difference (voltage) between the voltage applied to the anode 24 and the voltage applied to the focusing electrode 17 is applied between the two ends of the spacer 40. The cathode panel side of the spacer may be in contact with another electrode, e.g., the gate electrode, depending on the type of the display. In this case, a potential difference (voltage) between the voltage applied to the anode and the voltage applied to the gate electrode is applied between the two ends of the spacer. Therefore, it is desired that the spacer 40 has basically high resistance, in order that an excessive current does not pass the spacer 40.
FIG. 7A and FIG. 7B schematically show the orbits of electron beams in a pixel positioned in the vicinity of the spacer 40. In FIG. 7A and FIG. 7B, the partition wall, the spacer holding portion, and the interlayer insulating layer are omitted. As shown in FIG. 7A, electrons emitted from the electron emission portion 15 head for the luminescent layer 22. However, when electrons are emitted from the electron emission portion 15 in the vicinity of the spacer 40, a part of electrons may collide with the side surface portion of the spacer 40. Furthermore, as shown in FIG. 7B, a part of electrons which have passed through the anode 24 of the anode panel AP and collided with the luminescent layer 22 may be backscattered at the luminescent layer 22, and a part of the backscattered electrons may collide with the side surface portion of the spacer 40. When the electrons collide with the spacer 40, secondary electrons are emitted from the surface thereof. In the case where the amount of electrons which collide with the spacer 40 is different from the amount of secondary electrons emitted from the spacer 40, the spacer 40 is charged and exerts an influence on the orbits of electrons and, thereby, changes in brightness of pixels along the spacer 40 occur. Therefore, an antistatic coating 40B formed from a material having a secondary electron emission coefficient close to 1 is disposed on the side surface portion of the substrate of spacer 40A. Various materials, e.g., graphite and other semimetals, oxides, borides, carbides, sulfides, and nitrides, have been known as the material having a secondary electron emission coefficient close to 1. For example, nitrides of transition elements (transition metals) and germanium nitride are disclosed as the nitride in Japanese Unexamined Patent Application Publication No. 2000-192017.
If the spacer 40 is a complete insulating material as a whole, the electrical charge of the side surface portion of the spacer 40 may not be passed to the anode panel AP side or the cathode panel CP side and, thereby, changes in brightness of pixels along the spacer 40 occur. Consequently, the spacer 40 is required to have high resistance in order that an excessive current due to a potential difference between the voltage applied to the anode and the voltage applied to the gate electrode does not pass and the electrical charge of the side surface portion of the spacer 40 is passed to the anode panel AP side or the cathode panel CP side without a hitch. In the case where the substrate of spacer 40A is formed from an insulating material, the antistatic coating 40B is required to have some extent of electrical conductivity. The germanium nitride is an insulating material and the transition elements conduct electricity well. The above-described Japanese Unexamined Patent Application Publication No. 2000-192017 discloses that the volume resistivity of a film formed from germanium nitride is adjusted by adding a transition element or a nitride of a transition element.